But she was shocked when she dropped from a size 22 to a size 10 in a little over a year, and her teachers began expressing concerns for her health.

Cerys said: ‘I’d always maintained a healthy diet throughout my life even before I decided I want to lose the weight and so when I started to lose the weight so dramatically, it was a shock and I didn’t know what was happening.

‘My mum wasn’t sure what was going on either and often questioned how I was feeling and my energy.

She weighed 18 stone at the age of 16 before she decided to lose some weight (Picture: SWNS)After beating cancer she is now training to be a fitness instructor (Picture: SWNS)

‘I would say I felt fine, but was experiencing a lot of fatigue, which I put down to a busy day at school and exam stress, and I was cold all the time.

‘I had difficulty sleeping and would wake up several times during the night. This continued up to the point I went to my doctor who asked me lots of questions about my lifestyle and diet and seemed to miss my other symptoms, which is where the mistake was made.’